1. Field of the Invention
This invention relates to method and apparatus for stacking sheets of material and, more particularly, to a method and apparatus for the continuous stacking of paperboard blanks issuing from a corrugator where one order of blanks following another may be of a different size.
2. Description of the Prior Art
A corrugator produces an endless stream of sheets or blanks. The blanks issuing from one order to another may be of different sizes. This continuous flow of blanks has to be received and stacked. For this purpose there exists fully automatic stacking machines on which stacks are formed and indirectly carried off. The biggest drawback of most prior art stacking machines is that the stack of blanks is not perfectly formed. This creates a great deal of difficulty when the stacks of blanks are to be stored side by side. In most prior art machines the problem arises from the way the blanks are held on the machine while a preceding stack of blanks is being removed, or a last stack of blanks of a particular size is being formed prior to removal. These prior art machines included a gate which extends across the machine and keeps the stream of blanks from advanceing while a stack is being removed or formed. It is the accumulation of blanks in front of the gate that provides the opportunity for misalignment.
The method and apparatus for stacking described and claimed in U.S. Pat. No. 3,938,674 issued Feb. 17, 1976, corrected the problem of misalignment when it was caused by the temporary accumulation of blanks. This prior art stacking machine, however, cannot accept continuous order of blanks of different sizes from a continuous running corrugator. If the apparatus of U.S. Pat. No. 3,938,674 were used when the size of one order were different from the preceding one, the second order would interfere with the last blanks of the first order.
Accordingly, it is an object of the present invention to provide a method and apparatus which can be used to stack different sized orders of boards continuously.